As reported just about everywhere, during her Emmy acceptance speech Viola Davis quoted Harriet Tubman:

“In my mind, I see a line. And over that line, I see green fields and lovely flowers and beautiful white women with their arms stretched out to me over that line, but I can’t seem to get there no-how. I can't seem to get over that line.”

I've checked the usual sources but I've been unable to track down the original Tubman-authored source of this quote. Any assistance would be appreciated.

As you've probably noticed, a slightly modified version of that appeared in Sarah Hopkins Bradford's Scenes in the Life of Harriet Tubman (published 1869, though I think it first appeared in December of 1868), so it's least contemporaneous with Tubman's life (1822-1913).

Quote:

"And all that time, in my dreams and visions," [Harriet] said, "I seemed to see a line, and on the other side of that line were green fields, and lovely flowers, and beautiful white ladies, who stretched out their arms to me over the line, but I couldn't reach them no-how. I always fell before I got to the line." [p. 16]

About this book, Tubman's entry at Wikipedia notes, "One admirer, Sarah Hopkins Bradford, wrote an authorized biography entitled Scenes in the Life of Harriet Tubman. The 132-page volume was published in 1869, and brought Tubman some US$1,200 in revenue.[130] Criticized by modern biographers for its artistic license and highly subjective point of view,[131] the book nevertheless remains an important source of information and perspective on Tubman's life."

Milton Sernett discussed Bradford's work in his Harriet Tubman: Myth, Memory, and History (2007).

Quote:

Aware that white American had little interest in placing Harriet Tubman in the pantheon of venerated historical figures dominated by white men such as George Washington, Thomas Jefferson, and Daniel Boone, Sarah Bradford candidly acknowledged that some would sneer at what she called "this quixotic attempt to make a heroine of a black woman, and a slave." Bradford was therefore conscious of the need to inform potential readers of the efforts she had made to verify the subject matter of her book, regardless of how hastily it had been compiled. Much of interest had to be left out of the 1869 volume, Bradford declared. She had been unable to substantiate all the stories told her by Tubman and Tubman's friends and relatives.

Lacking a cache of Bradford manuscripts and research notes, we cannot say with certainty how her narrative was constructed from the evidence, written and oral, available to her. Bradford's primary soure was, of course, Tubman herself ... Just how much opportunity Bradford had to sit down with Tubman and witness firsthand her heroine's marvelous storytelling abilities is an open question. The two women did talk in Bradford's home in Geneva. Bradford's method in putting together her "little book" during 1868 was to employ small swatches of narrative text recasting Tubman's oral testimony, paraphrases of Tubman's words, and, in some cases, attempts to capture the flavor of Tubman's speech through the use of direct quotes ..." [pp. 113=114]